ran@ivax.doc.ic.ac.uk.doc.ic.ac.uk (Robert A Nicholls) (01/19/90)
I have a SOTA VGA/16 board with 512K RAM. Does anyone have information about
this VGA board. It uses a Tseng Labs chip set. Examining the source code of
Bert Tyler's FractInt public domain program I have managed to perform basic
graphic operations in some of the extended VGA modes (ie set mode, read/write
a pixel). However, I have not managed to use the 800X600 with 256 colours mode
properly. Using the method Bert Tyler uses for setting this mode on an Orchid/
STB/Genoa/Sigma board, I get a fractal image drawn in the correct mode, except
a few vertical lines appear in the image. These lines seem to be mapped to
RAM which does not contain constant values since the colours of the lines aree
constantly changing very rapidly. So the question is am I doing something wrong
or have I got some bad RAM? The diagnostic program that came with the board
shows everything as ok but I think it only uses the first 256K.
If anyone can help me with this problem or has information about doing such
things as panning and scrolling on this board, I would be most grateful.
Thanks,
Bob. eric@mks.com (Eric Gisin) (01/24/90)
In article <1460@gould.doc.ic.ac.uk>, ran@ivax.doc.ic.ac.uk.doc.ic.ac.uk (Robert A Nicholls) writes: > I have a SOTA VGA/16 board with 512K RAM. Does anyone have information about > this VGA board. It uses a Tseng Labs chip set. Examining the source code of > Bert Tyler's FractInt public domain program I have managed to perform basic > graphic operations in some of the extended VGA modes (ie set mode, read/write > a pixel). However, I have not managed to use the 800X600 with 256 colours mode > properly. Using the method Bert Tyler uses for setting this mode on an Orchid/ > STB/Genoa/Sigma board, I get a fractal image drawn in the correct mode, except > a few vertical lines appear in the image. These lines seem to be mapped to > RAM which does not contain constant values since the colours of the lines aree > constantly changing very rapidly. So the question is am I doing something wrong > or have I got some bad RAM? The diagnostic program that came with the board > shows everything as ok but I think it only uses the first 256K. I have seen these vertical strips on the Orchid Designer VGA (Tseng Lab too) when using VPIC to display images in 800x600 mode. We have had about 6 of these boards, and only one was semi-usable in 800x600 256-colour mode (it had faint vertical lines). Half of these boards had other problems in other modes. I think some board manufactures are using too slow memory. Our Designer 800 VGA (with extra 256K) does not have this problem The Designer has a pixel rate of 49.9 mHz, while the Designer 800 has a pixel rate of 35 mHz. This explains why the Designer 800 would work, it only requires a memory cycle time of 115 nsec, while the Designer requires 80 nsec. They require somewhat faster memory than the above figures because one in five memory cycles is usually allocated to read/write from the PC bus.